Buried interface and luminescent coupling analysis with time-resolved two-photon excitation microscopy in Ⅱ-Ⅵ and Ⅲ-Ⅴ semiconductor heterostructures

摘要

Semiconductor heterostructures are used in high-efficiency solar cells and in other electronic devices. Solar cells can’treach thermodynamic efficiency limits in part due to the charge carrier recombination, and efforts are applied to understandand reduce recombination. We describe a novel experimental approach to identify and quantify recombination losses atsemiconductor interfaces. Using time-resolved two-photon excitation microscopy, we generate carriers at well-definedabsorber depths and find that the red spectral shift of the photoluminescence (PL) emission can be used as a “spectroscopicruler” to identify recombination depth up to 30 μm. We apply this analysis to quantify Shockley-Read-Hall recombinationat the buried CdTe/CdTe interface, where 15 μm thick epitaxial CdTe is grown by the molecular beam epitaxy on thesingle crystal CdTe substrate. We also measure luminescent coupling between the GaInP and GaAs layers inheterostructures grown by the metal-organic chemical vapor deposition. Our results resolve important limitations foraccurate 3D charge carrier lifetime tomography. Earlier we analyzed recombination due to extended defects and grainboundaries with the lateral resolution sufficient to resolve such features (approximately 0.5 μm), but interpretation of thecarrier lifetime microscopy data for buried interfaces and buried semiconductor layers was a challenge. Using methodsdescribed here, the axial (z) coordinate for the PL microscopy measurements becomes as well defined as the lateral (x, y)coordinates, enabling accurate 3D identification and analysis of the charge carrier recombination locations insemiconductor heterostructures.